1. Field of the Invention
The invention relates to a rectifier module with a frame being open at the top and bottom forming a housing wall, a ceramic plate cemented to the frame forming a housing bottom, the ceramic plate having metallizations on a side thereof facing the housing interior which serve as conductor strips to solder semiconductor components, internal connecting straps and external connecting elements, the connecting elements being in the form of flat plugs which are freely accessible from the upper surface of the housing and are soldered to a metallization in the housing, and roughly half the housing is filled with a sealing compound.
2. Description of the Prior Art
Such a rectifier module is known from the brochure "BBC Heavy Duty Rectifier Bridges" DHS 104981/29D. In such a device, thyristors and diodes are used in particular as semiconductor components. Fully controlled and semi-controlled single-phase bridges can be built by means of such rectifier modules.
When the rectifier module operates at normal load, heat losses will occur inside the module housing. This causes the soft silicon sealing compound in the housing interior to expand more than the metallic flat plugs connected to the ceramic plate, because the coefficient of expansion of the sealing compound is higher by approximately one order of magnitude, so that the flat plugs are subjected to strong, cyclic tensile stresses. The flat plugs are soldered to the substrate with soft solder. Soft solders, however, react sensitively to cyclic stresses, so that there exists the danger that after many alternating stress cycles, the internal electrical connection between the connecting element and the substrate will be broken.
In addition, the heat developing during the operation of the rectifier module causes the ceramic plate to be locally thermally stressed through the metallizations which are heating up on the side of the ceramic plate facing the housing interior. This dissipation must be carried away toward the heat sink through thermal resistances that are as low as possible. The provision of a potential-free metal base plate does not bring the success hoped for, because this metal base plate will tend to become concave toward the center of the plate due to the "bimetal effect" when soldering the ceramic substrate/metal plate of the system with an intermediate layer of solder. Despite adequate application of heat conducting paste, the danger of the inclusion of thin air layers remains, increasing the thermal resistance between the metal base plate and the heat sink.
To avoid the latter disadvantage, the metal base plate is omitted in one known solution to the problem so that the ceramic is in direct contact with the heat sink. While this construction has fewer heat transfer points, it has the disadvantage of allowing the ceramic plate to be easily damaged in handling the module. The consequence would be a loss of insulating capability.
Building on this premise, it is accordingly an object of the invention to provide a rectifier module which overcomes the herein-afore-mentioned disadvantages of the heretofore-known devices of this general type, and in which the thermal stresses occuring during operation cannot lead to a defect of the module.